It is not uncommon for threaded fasteners, such as wood screws, machine screws and bolts, to break or to otherwise become so damaged as to preclude them from being disassembled or removed by ordinary means from the part to which they are secured. The prior art has addressed this problem and has proposed a variety of solutions, as evidenced by the disclosures of the following U.S. patents:
In U.S. Pat. No. 1,548,835, French proposes a device for removing broken wood screws, which has internal cutting threads and an external cutting element, the internal threads being employed to create a new thread on the remaining stub to enable its extraction.
In U.S. Pat. No. 1,683,796, Pearce describes an extractor for broken taps, which has ribs with tapered teeth for cutting and for engaging the tap grooves.
The device disclosed in Willis U.S. Pat. No. 1,848,590 has two working portions, and is used in two steps for extracting broken fasteners; it is initially employed to cut a plug into the material in which the fastener is embedded, and then a noncircular part of the tool is used to break away the plug.
Wolney U.S. Pat. No. 3,106,233 provides a tubular member which is mounted upon the blade of a screwdriver for axial adjustment of its position; it has a cutting end portion which is used to cut away the material surrounding the screw, to thereby permit engagement by the blade of the screwdriver for effecting removal.
In U.S. Pat. No. 4,204,308, Marling provides a screw extracting device having axially extending gripping fingers; the fingers are driven into the material, and are thereafter tightened upon the screw to effect its extraction.
The screw extractor of Drouin et al. U.S. Pat. No. 4,389,913 has a tubular extension at one end, with axially projecting cutting teeth; upon achieving sufficient penetration, a chuck component of the device is tightened to cause the fingers to grip the screw and thereby permit its removal, which is done in the opposite direction to cutting.
Accordingly, it is an object of the present invention to provide a novel extractor for threaded fasteners, which is of relatively simple construction and is yet highly effective for its intended purpose.
It is a more specific object of the invention to provide such an extractor, which is constructed to expand over a broken-off piece of fastener and to frictionally engage it for removal.
Another specific object is to provide such a device which is also capable of cutting into the embedded fragment, and to then distort so as to create the frictional engagement necessary for removal.
Additional objects of the invention are to provide an extractor having the foregoing features and advantages, which is relatively facile and inexpensive to produce, and is highly convenient and easy to employ.
A further object of the invention is to provide a novel method for extracting broken-off portions of threaded fasteners, which is fast, effective and convenient.